Optical films which are functional optical thin films used for, for example, light-transmissive films such as antireflection films, color filters, optical filters etc., are important and indispensable elements for displaying clear images on image display devices such as liquid crystal devices or plasma display devises.
Almost all such optical films have been prepared from inorganic compounds by film forming methods such as a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method. Examples using organic compounds have also been reported. For example, in Japanese Patent Publication No. 08-64492A, antireflection films prepared from metal-free phthalocyanines are disclosed.
It has been also known that functional optical thin films, optical elements and their raw materials can be manufactured from subphthalocyanines which are ring-contracted forms of phthalocyanines. For example, Japanese Patent Publication No. 2004-10838A discloses color resist inks and color filters used for emitting blue color. An aqueous blue ink for full-color printing of high bright colorfulness is disclosed in Japanese Patent Publication No. 2005-200601A, and a colorant that absorbs orange color light used for front panels of plasma display devices is disclosed in Japanese Patent Publication No. 2006-13226A. In addition, light-emitting devices using organic light-emitting diodes (LEDs) are disclosed in Japanese Patent Publication No. 2005-344021A.
Subphthalocyanines have been studied in an effort to apply them to various industrial fields such as pigment, thin film chemical materials, information recording materials, light emitting materials, etc.
However, subphthalocyanines of pigment have poor light resistance and poor solubility. Therefore, when thin films are required, it is necessary to prepare a pigment-dispersed liquid by dispersing the subphthalocyanines into a solvent and then apply the liquid to form a thin film. The thus obtained thin film made from such pigment-dispersed liquid cannot achieve sufficient transparency unless the subphthalocyanines are pulverized into an ultrafine homogeneous particle size of not more than 0.5 μm and with a very narrow particle size distribution. However, when the subphthalocyanines are pulverized into the ultrafine particle size region, the surface area thereof increases, causing further deterioration in light resistance. Furthermore, it is difficult to prepare homogeneous thin films if a liquid which contains a hardly dispersible pigment is used.
On the other hand, optical films such as functional optical thin films having light absorptivity in a specific wavelength region, antireflection films especially coated on marketable wide screen display panels such as plasma display panels (PDP) or liquid crystal display panels, color filters, optical recording media for using light of blue laser region, photoreceptors etc. are required to have a small half width in 530-580 nm of wavelength and also a sufficient light absorption properties.